The invention relates to a micropump and a microvalve which are small in size and are used in the medical field and analysis field for performing fluid control with high accuracy.
Conventionally, small-sized pumps for performing fluid control with high accuracy include, for example, a micropump described in Japanese Patent Laid-Open No. 1669/1993 and shown in FIG. 2, in which case a thin film 19 of metal or polysilicon is formed on a sacrificing layer of oxide film on a silicon substrate 1, and the sacrificing layer is removed by etching to provide a check valve of metal or polysilicon to provide a pump by a piezoelectric element 3 provided on a glass substrate 2.
Also, with a pump described in Japanese Patent Laid-Open No. 072270/1997 and shown in FIG. 3, a silicon substrate 1 having valve diaphragms 4 is joined to a glass substrate 2 and packings 6 are formed on valve seats 7 formed on the valve diaphragms 4. Voltage is applied on piezoelectric elements 3 disposed on the valve diaphragms 4 to deform the valve diaphragms 4 for opening and closing of valves on liquid inlet and outlet.
Also, a pump described in Japanese Patent Laid-Open No. 66784/1992 and shown in FIG. 4 is constructed such that two valves 7, respectively, serve as a one-way valve depending upon the positional relationship between the valves and fluid inlet and outlet 11. Therefore, liquid feeding is realized in one direction by applying voltage on a piezoelectric element 3 in a central portion for generation of volume change in the pump.
The above-mentioned pumps involve several problems. In the case of the pump construction shown in FIGS. 2 to 4, there has been the necessity of increasing an amount of volume change in pumping sections or drive frequency thereof in order to increase an amount of liquid feeding.
For the purpose of increasing an amount of volume change, a way to increase amounts of displacement for pumping diaphragms is conceivable, but since amounts of displacement of pumping diaphragms depend on amounts of displacement of actuators, it is not easy to increase such amounts of displacement while actuators of the same kind are used. Also, there is contemplated a way to increase such amounts of displacement by increasing an area of a pumping diaphragm, in which case there is caused a problem that a pump will become large in size and simultaneously pulsating flows will become large at the time of liquid feeding. Also, there is caused a problem that accuracy is degraded at the time of liquid feeding for a small amount.
Meanwhile, in the case where a pump is made small in size, a range, in which flow rate can be adjusted by drive frequency, is restricted since an increase in flow rate is not produced above a predetermined frequency due to that viscous resistance, which is generated when a fluid moves in the pump. Also, the pump shown in FIG. 2 or 4 is constructed in such a manner to use two one-way valves, and so involves a problem that a highly accurate adjustment of flow rate is difficult since flow generates toward an outlet side from an inlet side, in particular, when pressure acts in a forward direction toward the outlet side from the inlet side.
Also, with the construction of conventional pumps, the discharge volume per cycle is constant at all times and so fixed in flow rate. Therefore, there is caused a problem that the entire system is complex since it is necessary to use a voltage varying mechanism to change voltage supplied to actuators from a voltage source depending upon the driving condition when the discharge volume is to be modified.
The invention solve the foregoing problems in the conventional art pump of the invention, two substrates, the same substrate being formed with an inlet side valve section, a pumping section and an outlet side valve section, are joined to both surfaces of an intermediate substrate, and flow passages are provided to connect between a fluid inlet and two inlet side valves on the both surfaces of the intermediate substrate and between a fluid outlet and two outlet side valves on the both surfaces of the intermediate substrate. By the foregoing construction, two separate liquid feeding paths are formed on both surfaces of the intermediate substrate. Also, the two inlet side valves and the two outlet side valves are active valves, which can be opened and closed optionally by actuators and are constructed to be capable of being closed even in a state in which energy is not supplied. Therefore, liquid feeding can be performed with high accuracy without being affected by pressure changes outside the pump.
Further, with a method of driving a pump having the foregoing construction, a range of selectable flow rate can be enlarged while maintaining the same accuracy of flow rate as that of the prior art by using either of two liquid feeding paths in the case of a small flow rate and using [the] both liquid feeding paths simultaneously or at an optional timing in the case of a large flow rate.
Also, pulsating flows can be reduced at the time of liquid feeding provided that timing for liquid feeding in the two liquid feeding paths is appropriately selected.
Also, volumes of the pumping sections disposed on the both surfaces of the intermediate substrate and thicknesses of the diaphragms are made different from each other, then it is possible to change flow rate without a change in voltage applied to the actuators, that is, without the use of any special voltage varying mechanism.